Carbon monoxide (CO) poisoning within tents and snow caves is a real and probably overlooked problem. It is potentially an even greater problem at altitude because of the multiplicity of risk factors for CO toxicity. Despite multiple anecdotal reports of climbers perishing from CO poisoning on Himalayan peaks circulating in climbing circles, the danger does not appear to be widely recognized.

Diagnosing CO poisoning in the early stages may be difficult because of the nonspecific nature of symptoms and (at altitude) their similarity to AMS. The masking of symptoms when subjects are sedentary exacerbates the problem, and these are likely to be the occasions when individuals are subjected to the highest CO levels, such as resting and cooking in tents for hours during inclement weather. All attempts must be made to prevent CO concentration from reaching dangerous levels; safety can be enhanced by the use of small portable CO detectors.

Insidious onset of symptoms if sedentary (beware headache and fast heart rate, make regular trips outside to unmask symptoms, ventilate tent at regular intervals, ventilation does not have to be continuous)